1. Field of the Invention
The present invention relates to a method for manufacturing a semiconductor device which uses an alignment mark in order to cause an overlapping of a lower layer pattern and an upper layer pattern and, more particularly, to a method for manufacturing a semiconductor device which can prevent an alignment mark from being changed in shape.
2. Description of the Related Art
In a lithography step of a manufacturing process for a semiconductor device, in order to cause an overlapping with a high precision of a lower layer pattern and an upper layer pattern, there has hitherto been executed a method wherein an alignment mark is formed on the lower layer pattern and, using this alignment mark as a basis, a mask for use on the upper layer pattern is positionally aligned. FIGS. 1A to 1G are sectional views illustrating in the sequential step order a conventional method for manufacturing a semiconductor device.
In the conventional method for manufacturing a semiconductor device, first, as shown in FIG. 1A, an element isolating oxide film 101a and gate patterns 102 are formed on a semiconductor substrate 101 and a convex type alignment mark 103 is also formed thereon.
Next, as shown in FIG. 1B, an oxide film 104' having a thickness of, for example, 800 nm or so is deposited on an entire surface of the resulting semiconductor substrate by, for example, a chemical vapor deposition (CVD) technique. Then, by reflow, etchback, chemical-mechanical polishing (CMP) or the like, the oxide film 104' is flattened. As a result, a flat oxide film 104 is formed.
Thereafter, as shown in FIG. 1C, a photoresist 105 is coated on an entire surface of the substrate. Then, an exposure light 106 is radiated onto the photoresist 105 by a reduced projection type exposure apparatus through a contact-forming mask 107 disposed above the semiconductor substrate 101 and having a prescribed configuration. As a result of this, a contact opening portion 108 and an alignment mark opening portion 109 are simultaneously exposed. Then, the photoresist 105 is developed.
Subsequently, as shown in FIG. 1D, by the use of a dry etching technique, the portions of the oxide film 104 corresponding to the contact opening portion 108 and to the alignment mark opening portion 109 are removed to thereby open a contact hole 110 and simultaneously expose the alignment mark 103.
Next, as shown in FIG. 1E, a polycrystalline silicon film 111 having a thickness of, for example, 800 nm or so is deposited and thereafter the polycrystalline silicon film 111 is etched back by isotropic etching. As a result of this, the polycrystalline silicon film 111 is buried into the contact hole 110.
Then, as shown in FIG. 1F, a conductive layer 112 that consists of a WSi film having a thickness of, for example, 100 nm is deposited on an entire surface of the resulting substrate. And, a photoresist is coated on an entire surface of the resulting substrate. Then, an exposure light 114 is radiated onto the photoresist by the reduced projection type exposure apparatus through a wire-forming mask 115 disposed above the semiconductor substrate 101. At this time, the wire-forming mask 115 has a light-shielding portion at only a region aligned with the contact hole 110. And, by developing the photoresist, the photoresist 113 is caused to remain on a wiring layer forming predetermined region, e.g., the contact hole 110.
Subsequently, using the photoresist 113 as a mask, the conductive layer 112 is etched by anisotropic dry etching. As a result of this, as shown in FIG. 1G, a wiring layer 112' connected to the contact hole 110 is formed. Simultaneously, the convex type alignment mark 103 is exposed.
Thereafter, although not shown, using the thus-exposed convex type alignment mark 103 as a basis, a mask is positionally aligned to thereby form an upper layer pattern.
However, in this conventional method for manufacturing a semiconductor device, when etching the conductive layer 112, as shown in FIG. 1G, the convex type alignment mark 103 is inconveniently deformed. When the convex type alignment mark 103 is deformed, the precision with which the mask is positionally aligned becomes inconveniently decreased at the time of overlapping the upper layer pattern.
Also, in order to make it easy to detect an alignment mark, there has hitherto been proposed a method for enlarging a difference in level between the alignment mark and the semiconductor substrate (Japanese Patent Application Laid-Open No. Hei 1-149435). FIGS. 2A to 2D are sectional views illustrating in the sequential step order a conventional method for manufacturing a semiconductor device that is described in Japanese Patent Application Laid-Open No. Hei 1-149435.
In the conventional manufacturing method disclosed in this Publication, first, as shown in FIG. 2A, a glue insulating film 42 is formed on a semiconductor substrate 41 and, on the insulating film 42, a glue metal wiring layer 43 is formed as an alignment mark.
Next, as shown in FIG. 2B, an oxide film 44 is formed in such a way as to cover the glue metal wiring layer 43 and flattened. Thereafter, a photoresist 45 is coated onto an entire surface of the resulting substrate. And, simultaneously with the exposing of the contact hole, the glue metal wiring layer 43 and a portion surrounding it is exposed. Thereafter, the photoresist 45 is developed. As a result of this, the photoresist 45 aligned with the glue metal wiring 43 and its surrounding portion is removed.
Subsequently, as shown in FIG. 2C, the portion corresponding to the contact hole is etched and simultaneously the portions of the glue metal wiring layer 43 and its surrounding portion are etched to thereby expose an upper part of the glue metal wiring layer 43 from the oxide film 44.
Thereafter, as shown in FIG. 2D, an upper metal wiring layer 46 is formed and a photoresist 47 is formed thereon. And, alignment is done by the use of a laser light or the like.
Further, in order to prevent an alignment mark from being damaged, there has hitherto been proposed a method for forming a concave type alignment mark (Japanese Patent Application Laid-Open No. Hei 5-36600). FIGS. 3A to 3G are sectional views illustrating a conventional method for manufacturing a semiconductor device in the sequential step order that is described in Japanese Patent Application Laid-Open No. Hei 5-36600.
In the conventional manufacturing method disclosed in this Publication, first, as shown in FIG. 3A, concave type alignment marks 52 are formed at the surface of a semiconductor substrate 51 and then an etchback photoresist 53 is formed on an entire surface of the resulting substrate. The surface of this etchback photoresist 53 is flat and smooth. Also, the semiconductor substrate 51 and etchback photoresist 53 have approximately the same etching rate.
Next, as shown in FIG. 3B, a photosensitive resist 54 is coated on the etchback photoresist 53. It is to be noted that on the etchback photoresist 53 there may be formed an electron beam resist.
Subsequently, as shown in FIG. 3C, a mask is provided at a prescribed region located above the alignment mark 52, whereby as indicated by the arrow marks the photosensitive resist 54 is exposed with the use of an exposure light. In a case where an electron beam resist has been used instead of the photosensitive resist 54, electron beams are radiated.
And, by developing the photosensitive resist 54, as shown in FIG. 3D, the photosensitive resist 54 is caused to remain at a prescribed region located above the alignment marks 52. At this time, the etchback photoresist 53 is non-photosensitive and therefore is not removed and remains. Further, in order to cause the photosensitive resist 54 that has remained to have the same etching rate as that of the semiconductor substrate 51, the photosensitive resist 54 and the etchback photoresist 53 are both baked.
Thereafter, as shown in FIG. 3E, the entire surface of the resulting substrate is etched back as indicated by the arrows by dry etching such as reactive sputter etching.
At the early stage of this etchback step, at a prescribed region above the alignment marks 52 the photosensitive resist 54 is etched and at the other region the etchback photoresist 53 is etched. For this reason, after the photosensitive resist 54 has been etched, the etchback photoresist 53 is etched at the prescribed region. Accordingly, when the semiconductor substrate 51 has been flattened in said other region, as shown in FIG. 3F, the etchback photoresist 53 still remains to exist in said prescribed region. Namely, the alignment mark 52 is protected from being etched.
Next, as shown in FIG. 3G, by removing the etchback photoresist 53 remaining to exist, the concave type alignment marks 52 that have theretofore been protected are exposed. As a result of this, the flattening of the semiconductor substrate 51 is ended.
Also, in order to prevent the getting out of focus at the time of exposure, there has hitherto been proposed a method for manufacturing a semiconductor device that reduces the difference in height between a scribe line region and an element region (Japanese Patent Application Laid-Open No. Hei 2-211652). In the conventional manufacturing method described in this Publication, an insulating film and wiring film are caused to remain in the scribe line region, thereby preventing the misfocusing and the extending of cracks.
However, in the conventional method described in Japanese Patent Application Laid-Open No. Hei 1-149435, since in order to form a large difference in level even the glue metal wiring layer 43 itself is etched, the configuration of the convex type alignment mark is inconveniently deformed. For this reason, the alignment mark that is used for overlapping in the next lithography step becomes out of shape, raising the problem that the precision of overlapping decreases.
On the other hand, in the conventional method described in Japanese Patent Application Laid-Open No. Hei 5-36600, in order to protect only the alignment mark alone, the non-photosensitive resist and photosensitive resist are needed to be coated so as to protect the alignment mark and thereafter the photosensitive resist is further needed to be coated to thereby form a pattern. As a result, the coating of the resist is needed three times or more, raising the problem that the number of the manufacturing process steps increases and this causes a rise in the cost.
Further, in the conventional method described in Japanese Patent Application Laid-Open No. Hei 2-211652, it is difficult to stabilize the configuration of the alignment mark.